Bcl-2 family members are regulators of programmed cell death and appear to have causal roles in several human cancers. The functions of Bcl-2 proteins during the final minutes in a cell's life are the focus of intense effort to understand the underlying molecular details. However, the functions of Bcl-2 proteins in healthy cells are seldom investigated, despite increasing evidence that they have distinct "day jobs" that are crucial for normal cellular processes. For example, we have shown that the anti- apoptotic Bcl-2 family member, Bcl-xL, regulates mitochondrial morphology, mitochondrial fission and fusion, and synaptic activity in neurons, which we suggest will influence the initial steps in neurodegeneration. However, the molecular mechanism underlying this function is unknown, but is suggested to be a more evolutionarily conserved function of Bcl-2 proteins compared to their regulation of cytochrome c release. Cellular Bcl-2 homologues are also predicted to alter membrane curvature. Thus, Bcl-xL may influence mitochondrial dynamics by directly manipulating lipid membranes. I propose to determine if Bcl-2 family proteins have a direct role in membrane structure determination, and if they are involved in membrane fusion reactions. To accomplish this task, I will use defined lipids and recombinant proteins, as well as cell- cell fusion assays. PUBLIC HEALTH RELEVANCE: Bcl-xL and other Bcl-2 family members play a key role in promoting cancer progression and tumorigenesis by inhibiting apoptotic cell death. This is underscored by the development of small molecule inhibitors designed as anticancer agents that are currently in phase II/III clinical trials for the treatment of lymphoid malignancies, small- cell lung cancers and chronic lymphocytic leukemia. In addition, there is growing evidence that Bcl-2 modulate synaptic activity in healthy neurons by regulating mitochondrial membrane fusion/fission and mitochondrial localization, potentially influencing the initial steps in neurodegeneration. However, the biochemical function of these Bcl-2 family proteins that mediates these effects in neurons is essentially unknown and will be investigated here.